PURPOSE: To obtain high torque without using a decelerating means even when stress is applied from a means to be driven.

CONSTITUTION: In an ultrasonic vibrator 12 consisting of first and second resonators 7a, 7b transmitting ultrasonic vibration, a plurality of the piezoelectric elements 3 arranged between the resonators 7a, 7b and exciting ultrasonic vibration by the application of AC voltage and the clamping member 9 mutually bonding and fixing the resonators 7a, 7b and the piezoelectric elements 3, a plurality of the piezoelectric elements 3 are divided into a first piezoelectric element group 1 distorted in one direction and a second piezoelectric element group 2 distorted in other direction between the resonators 7a, 7b. By this constitution, an ultrasonic vibrator 12 exciting the distortion vibration of the resonators 7a, 7b and generating oval vibration in the end surfaces of the resonators by applying AC voltages different in phase to the resonators is obtained.